Flow structures in large-scale bank erosion zone of Lower Yangtze River.

This article focuses on the investigation of flow structures and turbulence characteristics in arc-shaped bank erosion zones along the middle and lower reaches of the Yangtze River, a process that poses significant risks to local residents and industries. Laboratory experiments using Particle Image Velocimetry (PIV) were conducted on scaled physical models representing two types of arc-shaped bank erosion—Type-I and Type-II—to capture three-dimensional velocity fields and analyze flow patterns. The study identifies three distinct zones within the erosion area: the backflow zone, mixing zone, and mainstream zone, with notable differences in flow exchange rates and backflow center positions between the two erosion types. A velocity distribution formula based on the Rankine vortex model was proposed for the backflow zone, revealing that velocity gradients in the peripheral zone are approximately four times greater than those in the central zone. The research highlights limitations related to model scale and measurement range, suggesting the need for larger-scale experiments and further study on sediment transport mechanisms to better understand and predict bank erosion development.